Re: [libvirt] [PATCHv3 1/2] network: added waiting for DAD to finish for bridge address.

On 10/16/2015 08:13 PM, Laine Stump wrote: > On 10/16/2015 12:51 PM, Maxim Perevedentsev wrote: >> On 10/15/2015 09:03 PM, Laine Stump wrote: >>> This loop *really* bothers me, because there is no failsafe to >>> terminate it if we never get positive notification that DAD has >>> completed. This would lock up the network driver startup, which >>> would lock up libvirtd startup. I think we need to decide on what >>> is the maximum time this could possibly take to complete (maybe it >>> is somehow based on the number of interfaces? or maybe it doesn't >>> matter...) and timeout from the loop after the appropriate iterations. >> I did not hear about general timeout for this operation. Maybe 5 >> min, for example? > > 5 minutes is a very long time when everything else is being held up. > If the wait for each network is much beyond a couple seconds, we'll > need to think about spawning off a thread to wait for DAD. > > (if you're curious where the single-threadedness is, look at > virStateInitialize() - it calls the stateAutoStart() function for > each subsystem driver in sequence, and within the stateAutoStart() > for the network driver, each network with autostart set is called in > sequence). I looked at kernel sources. It looks like DAD time is configurable: rand() % net.ipv6.conf.default.router_solicitation_delay [1s] + net.ipv6.conf.default.dad_transmits [1] * net.ipv6.neigh.default.retrans_time_ms [1000ms] By default on my machine, it gives 0s + 1 * 1000ms = 1s maximum. Kernel keeps track of DAD success (on timeout) / fail. We could take these variables from sysctl, but this is cumbersome. I suggest taking 5s as maximum timeout and hope this is not too long. Yes, I *really* do not want to write this thread-related stuff :)